The main goal of this Program Project is to bring together and strengthen the collaboration between six structural molecular biologists, in order to study problems in the structure, recognition, and assembly of biological macromolecules and macromolecular complexes. Specific projects to be examined include: a. X-ray analysis of selected synthetic DNA molecules, and their complexes with antitumor drugs and recognition proteins such as lac repressor and araC protein. b. Structure analysis of large, multisubunit enzymes in which information about one subunit affects behavior of another: glutamine synthetase, ribulose-bisphosphate carboxylase, and nitrogenase. c. Analysis of the individual protein components and of the intermolecular organization of the light-harvesting phycobilisomes of cyanobacteria. d. Study of ribosome structure and function using electron microscopy and x-ray diffraction. e. Examination of the factors that govern self-assembly and length regulation in T4 bacteriophage tail assemblies. The common theme that unifies these studies is the transfer of information from one macromolecular unit to another, whether in allosteric control, DNA recognition and repression, or interlocking and assembly in larger morphological units such as phycobilisomes, ribosomes, and bacteriophage. The shared facilities and intellectual interaction of the Program Project will aid in application of the most advanced methods of x-ray diffraction, electron microscopy, three-dimensional image reconstruction, computer graphics, and refinement.